SBRT holds the promise of curing early stage NSCLC

Stereotactic Body Radiation Therapy (SBRT), also known as Stereotactic Ablative Body Radiotherapy (SABR), has been in the spotlight for the treatment of lung cancer in the last few years. It holds the promise of not only curing early-stage operable non-small cell lung cancer (NSCLC), but does so with minimal toxicity and offers the patient more comfort and convenience. SBRT is a course of very high dose radiation treatment, capable of sterilizing or getting rid of the cancer with one to five abbreviated doses over one to seven days. This treatment dramatically reduces the inconvenience of six-week courses of conventionally fractionated radiotherapy.
“This is a treatment which requires considerable precision and accuracy because it is a very high dose of radiation and is not suitable for every type of cancer. What is important to ensure is that cancer is not near vital organs and the patient should not have had previous radiation to that area before. We have been using stereotactic radiotherapy to treat brain tumors for about 20 years but for lung cancer it is only in the past 10 years that it has become a popular method of treatment. It is usually preferred for cancers under 5cm in diameter, so for very large cancers it is not a very suitable treatment,” said Professor David Ball, Chair of Lung Service, Peter MacCallum Cancer Centre, Australia, and Member, APLCC 2016 International Committee. Dr. Ball is also the recipient of the Merit Award of International Association for the Study of Lung Cancer - IASLC (2011) and Editor-in-Chief, Journal of Medical Imaging and Radiation Oncology.

“One of the problems in using this method to treat lung cancer is that the cancer is usually moving during treatment as the patient is breathing in and out. Therefore, we are giving a highly focused and precise form of treatment to something that is moving. We overcame this problem by using four-dimensional CT scanning, which can map all the positions the cancer will occupy during the breathing process and target all possible positions, or only those positions for part of the breathing cycle (a process called ‘gating’),” Prof Ball added.

Can SBRT help in patients where cancer has spread to few sites?

“It is also feasible to give SBRT in cases where lung cancer has only spread to a very few sites (oligometastatic disease), is smaller than 5cm in diameter, and is in a location away from the heart or major blood vessels and airways, which could be damaged with this very high dose technique,” Prof Ball said. “We have commonly used SBRT for treating patients with oligometastases in the lung, as well as for oligometastases in the bones or adrenal glands, which in 90 percent of cases will sterilize the cancer. It might not stop the cancer from developing in other parts of the body but it will lengthen the period before the patient needs an additional treatment.”

SBRT and targeted therapies: Boon or bane?

“We have patients where cancer is effectively controlled by one of the new targeted drug therapies. However, if the cancer has spread to a few sites there is a possibility that one of the secondary cancers becomes resistant to the therapy, while the others continue to respond. We call this type of cancer “oligo-progressive.” In such cases, we do not want to change the medication as it is working on most of the secondary cancers except one site which can be considered for a dose of SBRT. We need to do randomized clinical trials to make sure that this approach does lengthen survival,” Prof Ball said.

Is the science of today the technology of tomorrow?

There is emerging evidence of the benefits of SBRT in managing early-stage NSCLC. Lack of randomized clinical trials, however, will keep raising valid questions, answers to which can only be found by science.

There have been two randomized clinical trials in the U.S. and the Netherlands to evaluate if using SBRT is as curative as surgery in early-stage NSCLC. NSCLC is not near the heart or major blood vessels or airway, but these trials had to be closed prematurely due to slow accrual. Surgery has a well-established role in the management of early-stage, operable NSCLC dating back decades. Thus, some patients may still prefer surgery. On the other hand, some patients may opt out of surgery because SBRT is painless (like an X-ray) and does not involve any anesthesia or the risks and dangers of surgery, and has minimal toxicity with better patient comfort and convenience.

“Unfortunately these clinical trials were too small to be conclusive and we need further studies to be done,” Prof Ball advocated.

“There are SBRT-related clinical trials commencing in North America and Europe and we may be joining one of these trials in Australia, too. Currently we have a research trial going on in Australia where we are comparing one dose of SBRT with four for oligometastatic lung cancer. We hope to show that one dose of SBRT is as good as four, which will be very convenient to the patient. Each treatment only takes under an hour to be delivered, no surgery or no anesthetic is required, and there is a 90 percent chance that cancer may be controlled,” Prof Ball concluded.